I have a purpose about the position of this level in the game. After the Tropical and the Circus zones, all characters goes to "Canadian" zone. However, if we play with Knuckles, near the begin of the level he falls in a trap made by Fang. Fang should catch Knuckles with a lasso and throw him into a chasm for example.

I think a such level perfectly match with Fang and his trapper facet. Then, this scene will be a wink at the trap tighted by Knuckles in Hydrocity Zone. In this case of course, the Canadian zone would be very short for Knuckles, as Hidden Palace Zone in Sonic & K. It also means Knuckles should be the only character who can pass through the first act of this area.

Sonic and Tails would pass throught Canadian zone but they could take a secret passage at the end of the act 1 (behind a waterfall ?) which leads to the act 2 of Underground Zone.

To resume:I/ The way of Sonic and Tails:
Circus zone -> Canadian zone Act 1 -> Canadian zone Act 2 or Underground zone Act 2 (if they have taken the secret passage).

The plan was to have the Canadian zone and the underground zone as split paths. This way when it came to the City zone which is next you would either come in on a raised motorway from the Canadian zone or come up from the sewer if you came from the underground zone